linux-kernel - Re: [Update][RFC/RFT][PATCH v3 2/5] driver core: Functional dependencies tracking support

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Message-ID: <CAJZ5v0h99yO8R28BkW-v3NZdc1GxupYx-4yeedduqpLfsxW01Q@mail.gmail.com>
Date:   Tue, 27 Sep 2016 13:52:48 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Mark Brown <broonie@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Luis R. Rodriguez" <mcgrof@...e.com>
Subject: Re: [Update][RFC/RFT][PATCH v3 2/5] driver core: Functional
 dependencies tracking support

On Tue, Sep 27, 2016 at 10:54 AM, Lukas Wunner <lukas@...ner.de> wrote:
> On Fri, Sep 16, 2016 at 02:33:55PM +0200, Rafael J. Wysocki wrote:
>> +void device_links_unbind_consumers(struct device *dev)
>> +{
>> +     struct device_link *link;
>> +     int idx;
>> +
>> + start:
>> +     idx = device_links_read_lock();
>> +
>> +     list_for_each_entry_rcu(link, &dev->links_to_consumers, s_node) {
>> +             enum device_link_status status;
>> +
>> +             if (link->flags & DEVICE_LINK_STATELESS)
>> +                     continue;
>> +
>> +             spin_lock(&link->lock);
>> +             status = link->status;
>> +             if (status == DEVICE_LINK_CONSUMER_PROBE) {
>> +                     spin_unlock(&link->lock);
>> +
>> +                     device_links_read_unlock(idx);
>> +
>> +                     wait_for_device_probe();
>> +                     goto start;
>> +             }
>
> While revisiting this function it just occurred to me that there's
> a theoretical infinite loop here if the consumer probes, is unbound
> by the supplier, then reprobes again before the supplier had a chance
> to update the link to DEVICE_LINK_SUPPLIER_UNBIND.  Perhaps this isn't
> a problem in practice, but noting anyway.

But the consumer is unbound only after setting the link status to
DEVICE_LINK_SUPPLIER_UNBIND and then it won't probe again.

Or am I overlooking something?

Thanks,
Rafael